Zinc organic compounds play an increasingly important role in organic synthesis in the production of pharmaceuticals, agrochemicals and other fine chemicals. Most of all because of their good compatibility with a variety of functional groups, they are important intermediates in organic chemistry. In addition to direct insertion of Zn metal into organic halides, they can be prepared by transmetallation of Li- or Mg-organic compounds. In special cases, a transmetallation of an organolithium compound using a solution of ZnBr2 and LiBr, for example in dibutyl ether, enables special transformations such as the stereoselective C-glycosylation of arylzinc reagents (S. Lemaire, I.N. Houpis, T. Xiao, J. Li, E. Digard, C. Gozlan, R. Liu, A. Gavryushin, C. Diene, Y. Wang, V. Farina and P. Knochel, Stereoselective C-Glycosylation Reactions with Arylzinc Reagents, Org. Lett 2012, 14, 1480-1483).
Zinc bromide and lithium bromide are prepared by the reaction of cheap raw materials such as zinc oxide, zinc carbonate, zinc metal, lithium hydroxide or lithium carbonate with hydrobromic acid in an aqueous medium. The solid salts are obtained by crystallization or evaporation of the reaction solutions. The solids thus produced are then dissolved in dibutyl ether.
For the transmetallation reactions named above, the most-anhydrous solution possible of zinc bromide and lithium bromide in dibutyl ether is required. To accordingly produce the anhydrous solids, long drying times and/or high drying temperatures are required. After drying, the solids must be packaged, and must likewise be dissolved in dibutyl ether in a manner which excludes moisture.
It would therefore be desirable to produce zinc bromide and lithium bromide from cheap raw materials directly in the desired solvent, dibutyl ether. The process should directly produce an anhydrous solution, or it should be possible to easily remove from the system any water of reaction which may form.